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Plant–Water Relations

  1. John B Passioura

Published Online: 15 FEB 2010

DOI: 10.1002/9780470015902.a0001288.pub2



How to Cite

Passioura, J. B. 2010. Plant–Water Relations. eLS. .

Author Information

  1. CSIRO Plant Industry, Canberra, Australia

Publication History

  1. Published Online: 15 FEB 2010
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Figure 1. Capillary action. Surface tension generates an upward pull on the water in the capillary tube. The water rises to a height of 1 m in a tube of radius 15 μm, or more generally to a height of 15×10−6/a m (eqns 3 and 4) for a tube of radius a (m).

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Figure 2. Instruments used to measure hydrostatic pressure of soil water. (a) Tensiometer. The porous ceramic cup allows water to move between the soil and the inside of the instrument. Eventually the pressures equalize and the pressure gauge of the instrument then gives the pressure in the soil water. (b) Pressure plate. Enough gas pressure is applied to the chamber to bring the water in the soil to atmospheric pressure, when it is on the verge of exuding from the outlet. The gas pressure is then equal and opposite to the original pressure in the soil water.

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Figure 3. Pressure chamber for measuring the water potential of a leaf. The leaf is cut from a plant and quickly placed in the chamber, with a small piece of it protruding through the pressure seal. As with the pressure plate (Figure 2), enough gas pressure is applied to the chamber to bring the xylem sap to the point of bleeding from the cut surface. Because transpiration has stopped, the xylem sap is close to equilibrium with the cells of the leaf and the applied balancing pressure is equal and opposite to that of the original pressure in the equilibrated xylem sap.